Wires, pins and rods are implanted by orthopedic and other surgeons in patients to aid in the alignment, reduction, and fixation of fractured bones. Wires, pins and rods are available in several standard lengths and in a range of diameters. Since an application may require a wire, pin or rod of a length that may not be available from a manufacturer, surgical cutters are used by surgeons and others to cut wires, pins, or rods to the desired length.
In the past, surgeons relied on hardware store quality cutters for cutting wires, pins and rods. Although manufactures of surgical instruments have now developed cutters more suitable for operating room applications, cutters still suffer from a number of limitations which cause the early breakdown of the cutters, and particularly the breakdown of the jaws of the cutter.
It is known in the art that quality jaws should be manufactured using a tough specially-tempered tool steel such as 400 series stainless steel. Quality jaws are currently manufactured from a 400 series stainless steel that is cut in cross-sections from large steel bars. A jaw that is manufactured from stainless steel that is cut in cross-sections from large steel bars has a cross-grained structure, which cross-grained structure is not best adapted to the increasing hardness of spinal rods which are used today by surgeons and which, hence, need to be cut by the cutters. In accordance with one aspect of the present invention, the jaws of the cutter are improved in that they are manufactured using 400 series stainless steel bar stock that has been rolled to the width and thickness of jaws so that the stainless steel in the jaw has a linear-grained structure. A jaw made from linear-grained structure stainless steel has a harder and thus longer-lasting jaw cutting edge.
The cutting edges of the jaws of prior art cutters have been hand-ground, resulting in slight inconsistencies in the geometry of the jaw cutting edge. These slight inconsistencies in the geometry of the cutting edge contribute to the early breakage of the cutting edge due to stress. In accordance with another aspect of the present invention, the jaws and jaw cutting edges are improved in that they are manufactured using Computer Numerical Control technology. Computer Numerical Control technology manufactured jaws and cutting edges are precise. The jaws have the same symmetrical settings along the entire jaw cutting edges. Cutting edges with precise symmetrically-machined angles require less cutting force than un-even hand-sharpened cutting edges since the flow of material (material displacement) is symmetric. Moreover, the jaws and the jaw cutting edges last longer because they can better withstand the stress of cutting.
Manufactures of cutters have recognized the necessity of placing an adjustable stop on the handle of a cutter to correctly calibrate the timing of the jaw shut-off (where the jaws naturally come together and stop) and handle-stop (such as where the jaws are stopped by an immovable/unadjustable bar on a handle). Because of the inconsistencies of the jaw cutting edge, the imprecise construction, and slight variances due to threaded bolt design, an adjustable stop was necessary to correctly set the timing of jaw shut-off and the handle-stop action of the cutter. Such adjustable stops allow individuals to adjust the point where the jaws meet and the maximum force or pressure that can be applied to the jaw edges before hitting the handle stop. With incorrect adjustment by an untrained individual, however, the time between jaw shut-off and handle-stop can be lengthened resulting in more force being placed on the jaw edges than the cutter is intended to endure during the cutting process and this ultimately will cause jaw overload and jaw breakage. In accordance with another aspect of the present invention, the cutter is improved in that the handles are designed with a precise non-adjustable stop. This feature protects the cutter from jaw overload. That is, in the improved cutter, the handle-stop (jaw shut-off) has been designed without an adjustment option, and the handle stop and jaw closure are precisely adjusted to cut a particular diameter wire, pin and/or rod correctly. The resulting cutting consistency contributes to a longer life for the cutting edges of the jaws.
The jaws of prior art cutters, with use, become increasingly tight because many of such cutters consist of two jaws which are held between two holding plates by two threaded bolts. Over time, the threaded bolts cause the jaws to actually bind and perhaps to stop functioning altogether. This binding adds stress on the bolts, which stress can result in shearing of the bolts especially at thread diameter. Moreover, since the spacing of the two holding plates is controlled by the pitch of the threading on the bolts, the spacing between the holding plates is not completely uniform and precise, causing additional stress. In accordance with another aspect of the present invention, the improved cutter resolves these problems by the use of a free "floating" bolt. The floating bolt is not threaded to the jaws or to the holding plates and it allows the jaws to freely pivot about the bolt. The floating bolt consists of a cap-bolt which is threaded into an internally threaded bushing. When the cap-bolt is fully threaded into the bushing, it secures the jaws/holding plate assembly together but nothing mechanically connects it to the jaws/holding plate assembly, hence it is a floating bolt allowing the jaws to freely pivot. Similarly, the floating bolt secures the jaw/handle assembly together but nothing mechanically connects the floating bolt to the jaw/handle assembly. The free floating bolts connected to the jaws prevent stress build-up and tightening on the jaws. The free floating bolts connected to the jaws also prevent binding or clamping of the holding plates to the jaws. The precise spacing between the jaw/holding plate assembly also prevents stress build-up and tightening. Stress on the bolts themselves is lessened and therefore the bolts are not sheared during cutting.
Several prior patents describe cutters and their features including U.S. Pat. Nos. 5,272,810 to Orthey, 4,910,870 to Chang; 3,340,611 to Lauck; 3,315,669 to Rhodes; 1,472,392 to Harvey; 1,145,082 to Porter; 914,910 to Alley; 790,617 to Carolus; and 444,541 to Porter. None of these patents, however, employ the improved features and structural configuration of the cutter of the present invention.